Generating and modulating system



Nov. 3 1925- 1,559,870

R. A. HEISING Filed Feb. 27. 1920 lnvenTor: Raymond A. Hal's/mg.

Any

Patented Nov. 3, 1925.

UNITED STATES PATENT OFFICE.

RAYMOND A. HEISING, OF EAST ORANGE. NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

GENERATING vAND MODULATING SYSTEM.

\ Application filed February 27. 1920. Serial No. 361,864.

To all whom it may 0011 new Be it known that I, RAYMOND A. Hnrsme, a citizen of the United States. residingat East Orange. in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in'Generating and Modulating Systems, of which the following is a full, clear, concise, and exact description.

The invention relates ,0 modulating systems and more particularly to generating and modulating systems of the type wherein are employed vacuum tubes having anodes, cathodes and discharge control elements, or equivalent space discharge devices for the generation and modulation of oscillations.

The principles of the invention are applicable in various systems but are particu larly applicable in systems of the type wherein a vacuum tube or set of vacuum tubes functions to generate oscillations and another tube or set of tubes having a space current source in common with'the first set acts to vary the voltage supply of the first tube or set of tubes to cause modulation or variation in amplitude of the waves generated. It is frequently desirable in modulating systems that the second tube or set of tubes, which will, for brevity, be herein referred to as the variable impedance tube, be a duplicate of the oscillating tube or system of tubes. The ideal variable impedance tube or device in such a case will be one whose impedance varies from zero to infinity. This would produce the most complete modulation. In practice, however, the impedance of a tube capable of efficiently generating oscillations would never so vary and hence it would be undesirable for use as a variable impedance. Suppose in such a system that the normal voltage supply is 350 volts and the voltage across the varlable' impedance tube at the lowest value is 150 volts, then the least voltage across the oscillator is 150 volts. If the oscillator continues, at this voltage, to generate oscillations of a substantial amplitude, the modulation will not be complete.' One object of this invention is to overcome this difliculty and thus to produce more nearly complete,

modulation.

However, this invention is not limited in application to the case of identical variable impedance and oscillatory tubes since variable impedance tubes of the ideal type have not, as yet, been produced andmould if available for use produce other undesired results even if combined with an efiicient oscillator.

The invention from one aspect comprises an auxiliary power source for use with a modulating system comprising an oscillator and a variable impedance device where the oscillator and the variable impedance device constant current type for causingthe current supply to divide unequally between the oscillator and the variable impedance device.

Either the oscillator or the variable impedance system may include a single vacuum tube or equivalent device or a. number of dleivices arranged either in series or para -el.

Referring to the accompanying drawings, Figure 1 is a curve illustrating the type of modulation upon which the present system is intended to improve; Fig. 2 is adiagram hereinafter referred to in explaining the invention, Fig. 3 illustrates a constant current modulator having the invention an plied thereto, Figs. 4, 5 and 6 illustrate modified forms, the oscillator in each of these figures being illustrated by a square.

In Figure 1 is illustrated a high frequency waveX modulated in accordance with a low frequency speech wave Y.

Since the curve Y representing the speech wave nowhere touches the zero axis, the modulation is "not complete.

Fig. 3 comprises an oscillating tube 5, directly connected so as to generate osclllations in the antenna circuit 6. A space eurrent circuit for the tube contains a'suitable source 7 in series with the speech frequency coil 8 and the high frequency choke 9;

.by vertical coordinates and the potential diflerence E in volts between the cathode and the anode by horizontal coordinates. As shown by this curve, when the voltage across the variable'impedance tube 2, which is the same as the voltage across the oscillator, reaches its lowest value such as, for example, 150 volts, oscillations of considerable amplitude would still occur as indicated by the minimum amplitude -of the curve X in 1. The battery 13, however, is included in the space current circuit of the tube 5, so

as to oppose the source 7. the source 13 has a voltage of approximately 100 volts, then it has an effect similar to that which could be represented by displacing the curve a, in Fig. 2, to the right to the position of the curve Z). The minimum amplitude of the oscillations produced by the generator will therefore approach closely to zero and may, if desired, be made to become zero if the battery 13 is of sufficient voltage.

In Fig. t instead of placing the battery 13 in circuit with the oscillator a battery 13' is placed in circuit with the variable impedance tube and poled in such a direction as to aid the source 7. The eflect produced is similar in the two cases and this arrangement has the additional advantage that current is not being forced backward through any battery of the system which is truein the case of the battery 13 in Fig. 3.

In the arrangement of Fig. 5, an auxiliary source is not used. In place of it a resistance M is placed in the anode-cathode circuit of the oscillator and made of such a value as will cut down the potential difference across the oscillator to a suitable value. In order to allow the speech frequency variations to pass without attenuation, the condenser 15 is shuntedaround the resistance 14.

The arrangement of Fig. 6 comprises, in efiect, acombination of those in Figs. 3 and d. lln the lead to the oscillator, is connected a motor M which is connected mechanically, by any suitable means 16, to drive a generator G in circuit with the variableimpedance device. The fields of the motor and generator should be separately excited either by individual circuits, or as illustrated, by a common circuit 17. Condensers l5 allow speech frequency variations to be shunted around the generator and the motor. The back electromotive force of the motor M reduces the voltage across the vacuum tube generator while the electromotive force produced by the mechanical generator G increases the voltage across the variable impedahce device. The motor, in effect, extracts energy from the oscillator circuit and supplies it to the variable impedance circuit.

An amplifier having a separate carrier frequency input source may replace the oscillator 5 which is in eflect an amplifier repeating its own output waves.

The invention is not limited to any particular form of oscillator or embodiment herein described, but certain features and parts thereof may be embodied in other constructions and utilized in other systems. lit is to be understood also that the invention is applicable to transmission systems other than those employed for signaling and to systems using line wires as well as radio systems. The novel features believed to be inherent in the invention are defined in the appended claims.

What is claimed is:

1. A modulating system comprising a plurality of discharge devices in parallel with respect to a common source of energy supply therefor, appropriate circuits whereby one of said devices generates oscillations, means for varying the impedance of'the other device at a relatively low frequency rate, and an energy consuming device in circuit with the oscillating device for causing the potential difference thereacross .to be less than across the variable impedance device.

2. In a==syste1n according to claim 1, a

across said devices to be of different value.

i. A radio; transmission system comprising aspace discharge device for amplifying in its output clrcurt high frequency waves impressed upon its input circuit, a variable impedance space discharge device connected to said first mentioned device for varying the amplifying power thereof, each of said discharge devices having a cathode, an anode and an impedance control element, space current circuits for said devices connected between their respective cathodes and anodes, and means in said circuits for deriving energy from the space current circuit across the terminals of said modulating de;

vice, a sourceof electromotive force for supplying space current to sald dev1ces, and means for causing a back electromotive force in the circuit of one of said devices.

- device for causing a drop of whereby the completeness of modulation of the modulated waves produced may be materially increased. I

6. A modulating system comprising a modulating device, a variable impedance device, a source of current for supplying said devices, means whereby the sum of the cur rents supplied from said source to said de-. vices is maintained substantially constant, and means in the circuit of said modulating (potential other thanf'the drop acrbss the mo ulating device itsel 7. An electrical syste m comprising a plurality of space discharge devices, a source of electromotive force, means whereby the sum of the currents supplied to said devices from said source remains substantially constant, and means for making the potential difierence across one of said devices substantially larger than the potential diiference across another thereof. I

8. A modulating system comprising a modulating discharge device, a variable impedance discharge device, a source of current for supplying said devices, and a motor in circuit with one of-said devices driven by the currents supplied thereto. 9. A system "for converting electrical waves into Waves of other wave form comprising a wave converting device, a variable impedance device controlling said converting device, a source of electromotive force for supplying current to said devices, a generator in circuit with said variable impedance, device for supplying additional current thereto, and an alternating current by-pass around said generator.

' 10. A system comprising two thermionic space discharge devlces, a single source of,

electrical energy for supplying said devices,

'a device in circuit with one of said devices driven by a current passing therethrough, and another device in the circuit of the other of said devices driven .by the first named current-driven device. 11. An electrical system for utilizing both the direct a and alternating components-of a fluctuating uni-directional current which comprises a motor driven by the direct current component, a device in Seriestherewith controlled in accordance With'tlie amplitude of the alternating current component, and an alternating current by-pass in shunt to said motor.

12. An electrical system comprising a pluralitv of space discharge devices, a source "of electromotive force for supplying said devices, means for maintaining substantially constant the sum of the currents supplied to said devices from said source, and an auxiliary sourc for making the otential difierence across one of said devlces substantially larger than that across another thereof.

13. A source of current, a plurality of circuits supplied in parallel with current from said source, means for maintaining the sum of the currents in said circuits constant, current operated devices in said circuits respectively, and a source of potential for maintaining the potential difierence across one of said devices difierent than across another of said devices.

14. A source of current, a plurality of circuits supplied in parallel with current from said source, means for maintaining the sum of the currents in said circuits constant, current operated devices in said circuits respectively, and means for maintaining the tential difierehce across one of said. devices ifierent than across another of saiddevices;

15. A source of current, a plurality of circuits supplied with current in parallel from said source, means for keeping constant in said circuits the sum of the currents supplied from said source, and an auxiliary source of potential in one of said circuits opposing the electromotive force of said firstmentioned source of current.

In witness whereof, I hereuntofsubscribe my name this 25th day of February A. D., 1920.

'RAYMOND A. IIEISING. 

